b. After the rotor control has completed its boost cycle and the tube anode is up
to speed, signal OHO from the rotor control energizes signal BUC through the interlock
and safety relay. This causes back-up contactor K2 to close through relay K3 contacts
BUC/BUL and through relay Re-4-BT contacts BUL/BPL. When the EXPOSE button is
pressed the following occurs.
(1) The H6 (rotor control CFD 7.0) goes to 115vac and becomes H6T, after
passing through contacts H6/H6T of the relay Re-4-BT.
(2) The H6T then goes to the impulse timer. Signal BAM from the impulse timer
immediately goes high, activating relay K1.
(3) This removes the short from the back-up timer capacitor C1, and the
cathode of the SCR connects to the common.
(4) Timing immediately commences, with C1 charging through selected
resistors on the timer switch, and potentiometer R2.
(5) When C1 charges to a voltage to the reference set by the potentiometer
R9, the unijunction transistor Q2 discharges the capacitor C1 through its emitter/base
junction, providing a gating signal to the SCR.
(6) The SCR turns on, activating relay K3. This causes BUC to break from
BUL and switch to BPT, forcing the back-up contactor K2 to release and relay Re-4-BT
to energize.
(7) Contacts XBR/XD are also made, which cause the filament-standby
resistor to be returned to the circuit and reduce the filament to standby level.
c. Concurrently Re-4-BT is energized by BPT. This causes contacts H6/H6T to
break, terminating the exposure signal to the impulse timer.
d. When automatic exposure control is employed and terminates the exposure,
BAM immediately goes low, deactivating relay K1. This shorts the timing capacitor C1
and inhibits completion of timing cycle. In these circumstances, the back-up contactor
K2 remains engaged until signal H3 is released by releasing the PREPARE button or
advancing the cassette to the parked (fluoro) position during spot filming.
e. The voltage level on the charging capacitor, at which the unijunction transistor
triggers the SCR, is adjusted by potentiometer R9 (overall-time adjust). This adjustment
provides a proportional increase or decrease in the back-up time interval for each time
selection. Potentiometer P2 (short-time adjust) is in the charging resistor path. It
increases or decreases the timer interval by a fixed amount for each time selection.
MD0351
2-25
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